Process for making vacuum fixtures for miniature magnetic memory cores



Oct. 26,l965 J. FRA ZEN, JR 3,214,273

PROCESS MAKING CUUM FIXTURES FOR MINIATURE MAGNETIC MEMORY CORES Filed Oct. 25, 1961 f fi I/Z\ /7/I/E\ z 0 F/6.4 N l 1 2/ Y W Z 147 o/e/vfr United States Patent 3,214,273 PROCESS FOR MAKING VACUUM FIXTURES FOR MINIATURE MAGNETIC MEMORY CORES John J. Frantzen, In, St. Paul, Minn., assignor to Buckbee- Mears Company, St. Paul, Minn., a corporation of Minnesota Filed Oct. 25, 1961, Ser. No. 147,513 8 Claims. (Cl. 9636) This invention relates to a process for making a vacuum fixing which is particularly :adapted for use in assembling and holding thousands of minute ferrite cores of rectangular shape in cross section. My process is particularly useful in the production of such fixtures having cavities ranging in length from .150 to .005 inch and from .075 to .002 inch in width, located and of a selected, uniform size within tolerances of plus or minus .0005 inch. The cores to be held in such cavities are of short tubular shape adapted to have circuit conductors threaded through them while the cores are held in the fixture. Such a memory system may comprise from two thousand to five thousand cores which must be accurately located in an area of less than 16 square inches. Heretofore, attempts to provide fixture cavities for the cores of such memory systems have not been entirely successful due to the difficulties attendant upon forming cavities of such small sizes and shapes defined by straight sides and of the requisite uniform size and location. The cost of making such fixtures according to known procedure has been exceedingly high.

It is, therefore, an object of my invention to. provide a process for forming such vacuum fixtures which meet the exacting requirements of cavity sizes, shapes and tolerances.

A further object is to provide a process for producing such miniature magnetic core nest fixtures at a greatly reduced cost as compared with the processes heretofore used in the manufacture of such fixtures.

The invention also includes certain other novel features of procedure which will be more fully pointed out in the following specification and claims.

According to my invention, a plate of photopolymer material of uniform thickness, usually within the range .002-.08 inch thickness, is bonded to a backing layer of metal or other suitable material and is photo-printed on its normally upper face with the images of a multiplicity of cavity areas. For this operation a negative, film having opaque areas defining cavity areas is placed in contact with the photopolymer plate in a vacuum printing frame and the film is exposed to a strong actinic light which is spaced sufficiently from the plate so that the light rays are directed substantially perpendicularly to the surface of the plate. A strongpultra-violet are light may be placed at a distance of 80 inches from the film and the exposure may be made for approximately 10 minutes, for example.

As the next step the unexposed areas of. the, photopolymer plate are washed out using sprays, containing about 190 cc. of 50% sodium hydroxide to. 25 gallons of water. This development treatment may be continued for a period from to minutes. The plate is then rinsed thoroughly with tap water and is air dried. Since the photopolymer plate may be slightly jelled at the edges of the cavities, I correct this condition by. replacing the plate in the printing frame and photo-printing it with the same negative opaque areas in registry with the cavities and exposure from 10 to 15 minutes to the light source. This hardens the walls of the. cavities which are straight and perpendicular to the normally upper face of the fixture plate.

As the next step, the backing sheet or layer which may,

for example, be a. stainless steel sheet on the order of .005 to .008 inch thick is formed with a perforation communicating with each. of the cavities from the back or normally lower side of the plate. This perforating of the metal backing layer is preferably done by photo: printing and etching. Thus a coat of photo-sensitized enamel is placed on the metal backing sheet and the WQIk is inserted between a set of negatives that have the memory core pattern on one side, and on the opposite, or metal sheet side, a dot pattern having each dot in registry with a cavity in the photopolymer plate. The, negative film sandwich thus formed is placed in a, vacuum frame and exposed to actinic light at the dot side only. The enamel coat is then developed by washing out the unexposed dot areas and the metal backing sheet is etched through at the dot, areas to form the perforations. Stainless steel or other suitable metal backing sheets may be etched by using a ferric chloride solution. This operation of perforating the metal'backing sheet may be performed either before or after the photoprinting and developing of the cavities in the photopolymer plate.

The fixture thus formed may be used asv the cover plate of a vacuum chamber from which air is exhausted to create the desired vacuum for drawing a minute core into each of the cavities and for retaining the cores. there.- in during the threading of they conductor wires through the openings in the cores, as hereinafter described.

Referring to the accompanying drawing:

FIGURE 1 is a plan view showing a blank photopolymer plate in which the minute cavities are to be. formed;

FIG. 2 is a plan view showing asfragmentary portion of a. completed fixture, on a greatly enlarged scale;

FIG. 3 is a cross sectional view showing a. fragmentary portion of the blank photopolymer plate and. backing' sheet bonded thereto;

FIG. 4 is a composite sectional view showing fragmentary portions of suitable photographed films infspaced relation to a photopolymer plate with cavities and a backing sheet before the perforations are formed therein;

FIG. 5 is a vertical sectional view showing a fragmentary portion of the finished fixture, and

FIG. 6 is a similar view of the fixture in place on a vacuum chamber and with a group of memory cores in place in the cavities.

In the drawing, the numeral, 10 indicates-a. photopolymer platehaving a backing sheet 11, permanently bonded to its lower side. The backing sheet is preferably formed from etchable material, such as, stainless steel or other sheet metal. The plate 10 may be formed fromfDycril, a Du Pont letterpress plate of thickness within the. range .002 inch to .08 inch. A multiplicity of rectangular cavities 12 are formed in a predetermined pattern arrangement by my improved process. Each of thesev cavities is formed to receive and fit the periphery and-sides of a single,. generally cylindrical core member 13. A perforation 14 for the withdrawal of air from the. cavity is. formed in backing sheet 11 in communication with the cavity. To facilitate precise location of the blank plate 10 with its backing sheet 11 in the printing frames and in relation to the photographic films, the blank is formed with indexing holes-10a, as indicated in FIG. 1. The core members 13 may be formedfrom a ferrite material, such as Ferramic, for example. Such core members have plane parallel opposite side faces and longitudinal side walls of the cavities 12 must fit accurately against the side faces of the. core members. The length of each rectangular cavity 12"must be such-as to: accurrately fitthe periphery-of a core member 13 when it is resting on the backing sheet 11 in the finished vacuum fixture.

with the enamel coat r18 in a vacuum frame.

My process utilizes a plane, fiat photopolymer plate having a metal hacking sheet 11 honded thereto, as indicated in FIGS. 1 and 2. A negative film, indicated at 15 in FIG. 4, is prepared with opaque areas 1 6 defining the areas of the rectangular cavities 1 2. These opaque areas are separated by translucent areas 17 defining the areas of the plate hetween cavities. The film .1'5 is used in a vacuum frame to photo-print the images of the cavities on the plate 10. In this photoprinting a source of actinic light of suitable intensity should be spaced from the film 15 a distance of 80 inches or more. The exposed areas of the polymer plate are thereby rendered insoluhle and the unexposed areas remain soluble to the full thickness of the plate 10 during the subsequent development treatment. The unexposed cavity areas are then washed out by the use of sprays containing a solution of NaOH to form the cavities 1 2. This photo-printing and developing proceduremay be repeated in order to solidify the walls of the cavities.

As the next step, a coat 1 8 of photo-sensitive enamel is applied to the lower side of the backing sheet 1 1, and a photographic film 19 having a pattern of opaque dots 20 is placed in registry with the cavities 12 and in contact The film is then exposed to actinic light to photo-print the images of the dots 20 on the enamel coat 18. The work is then removed from the vacuum frame and the unexposed areas defined by the dots 20 are developed to form openings in the enamel extending to the backing sheet 11. Etching to form the perforations 14 follows. Each cavity 12 is thereby formed with a perforation .14 for the withdrawal of air when the fixture is in use, and the top of the cavity is closed by a core 16.

As shown schematically in FIG. 6, the finished fixture may he used as the top closure of a vacuum chamber 2 1 from which air is withdrawn. The core members 13 are assembled in the cavities 1 2 by placing a multiplicity of core members on the upper face of the plate '10 and vibrating the latter while a suitable vacuum is maintained in the cham ber 21. The vibration causes the cores to roll and turn until each of them falls into one of the cavities ll Z where it is held by the withdrawal of air through the perforations 14. While so held, circuit wires 22 may he threaded through the central openings in the cores. Two or more of such wires may be threaded through each core to provide the required circuitry. To make this feasible, more than half the diameter of each core must project from the top of each of the cavities 12, as indicated in FIG. 6.

'. By this process l reduce the cost of making vacuum fixtures for holding such minute ferrite cores to a small fraction of the cost of making them hy previously known methods. The fixture cavities produced by my method are greatly improved in the matter of maintaining close tolerances in the uniformity of dimensions, shape and location of the thousands of cavities required in a unitary fixture 'of small size for the magnetic cores of recently improved memory systems.

I claim:

1. A process for making a nest for holding annular magnetic cores while wires are strung through their openings out of a photopolymer plate bonded to a rigid backing layer of a diiterent material comprising the steps of (a) photoprinting a multiplicity of the images of rectangular cavity areas each having a long and a short dimension on said plate from a negative film having opaque areas defining the cavity areas by placing said film in contact with said photopolymer plate and then exposing the plate through the film so placed to an actinic light source sufiiciently spaced from the plate to form insoluble exposed areas and soluble unexposed core cavity areas, and continuing such exposure until the soluble areas extend through the photopolymer plate to the backing layer, and

(-b applying solvent to the plate until those portions of the plate underlying said unexposed areas are completely washed out forming substantially straight walled core cavities extending to the depth of the depth of the underlying layer, the depth heing related to the other dimensions such that the cores wi-ll nest on edge in the cavities with most of the annular opening extending a-bove the surface of the plate.

2. A process in accordance with claim 1 which further includes the step of placing the negative film of step (a) in registry with the cavities formed and repeating the exposure of the film to actinic light until the walls of the cavities are hardened.

3. A process for making a magnetic core nest for a multiplicity of tubular ferrite cores in accordance with claim 1 in which the negative film used in step (a) contains more than one thousand precisely rectangular opaque areas defining the cavity areas and the thickness of said photopolymer plate is substantially less than onehalf the diameter of the magnetic cores to be contained therein.

4. A process for making a magnetic core nest in accordance with claim 1 wherein the thickness of the photopolymer plate is within the range O02.08 inch and the negative film used in step (a) contains a multiplicity of opaque rectangular areas each of a width within the range .075 to .002 inch and of a length within the range .150 to .005 inch.

5. A process in accordance with claim 1 further including the step of perforating through the backing layer at each of said core cavities thereby providing an opening for the withdrawal of air from the several cavities for seating and holding miniature cores in said cavities.

6. A process in accordance with claim 1 in which said backing layer is an etchable metal sheet and further including the step of etching apertures through said sheet into each of said core cavities.

7. A process for making a magnetic core nest vacuum fixture from a photopolymer plate bonded to a rigid backing layer which comprises:

(a) photoprinting a multiplicity of the images of rectangular cavity areas on said plate from a negative film having opaque areas defining the cavity areas in contact with said plate by exposing the plate when in said contact with the film to an actinic light source of sufiicient intensity to form insoluble exposed areas and soluble cavity defining areas on the plate and continuing such exposure until the insoluhle areas are extended through the plate to the backing layer;

( b) etching away the soluble material of the plate underlying the unexposed areas .by spraying the plate with a solvent until straight walled cavities are formed through the plate to the backing layer at the unexposed areas, the cavities having dimensions such that an annular core nesting on edge in the cavity will seat firmly against opposite end walls of the cavity with most of the opening through the coreextending above the surface of the plate; and

(c) etching a small aperture through the backing layer into each of the core cavities for providing a passageway for the withdrawal of air from the cavity for holding the cores in snug seating engagement within the respective cavities.

8. A process in accordance with claim 7 in which the etching of said backing layer includes the steps of first coating said layer with a light-sensitive enamel, then photo-printing on the enamel a pattern of opaque dots severally in registry with the cavity areas of the photo polymer plate, then washing out the unexposed dot areas of the enamel and then etching through the backing layer at the thus exposed surface areas of said layer.

(References on following page) 5 6 References Cited by the Examiner 2,830,899 4/58 Br-o'wn 96-3-6 NITED AT P A ENT 2,868, 124 1/ 59 Crawford 96- 35 X U ST ES T S 2,985,948 5/'6\1 Peters 340174 2,543,013 2/511 s X 3129098 4 64 Kitson 9 6-35 2,543,046 2/5'1 Murray 963 6 5 2,760,863 8/56 Pla'mbeck NORMAN G. TORCHIN, Primary Examiner.

2,827,690 3/58 Garrigus.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,214,273 October 26, 1965 John J Frantzen, Jr,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 4, strike out "depth of theh Signed and sealed this 31st day of May 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER 7 Attesting Officer v Commissioner of Patents 

7. A PROCESS FOR MAKING A MAGNETIC CORE NEST VACUUM FIXTURE FROM A PHOTOPOLYMER PLATE BONDED TO A RIGID BACKING LAYER WHICH COMPRISES: (A) PHOTOPRINTING A MULTIPLICITY OF THE IMAGES OF RECTANGULAR CAVITY AREAS ON SAID PLATE FROM A NEGATIVE FILM HAVING OPAQUE AREAS DEFINING THE CAVITY AREAS IN CONTACT WITH SAID PLATE BY EXPOSING THE PLATE WHEN IN SAID CONTACT WITH THE FILM TO AN ACTINIC LIGHT SOURCE OF SUFFICIENT INTENSITY TO FORM INSOLUBLE EXPOSED AREAS AND SOLUBLE CAVITY DEFINING AREAS ON THE PLATE AND CONTINUING SUCH EXPOSURE UNTIL THE INSOLUBLE AREAS ARE EXTENDED THROUGH THE PLATE TO THE BACKING LAYER; (B) ETCHING AWAY THE SOLUBLE MATERIAL OF THE PLATE UNDERLYING THE UNEXPOSED AREAS BY SPRAYING THE PLATE WITH A SOLVENT UNTIL STRAIGHT WALLED CAVITIES ARE FORMED THROUGH THE PLATE TO THE BACKING LAYER AT THE UNEXPOSED AREAS, THE CAVITIES HAVING DIMENSIONS SUCH THAT AN ANNULAR CORE NESTING ON EDGE IN THE CAVITY WILL SEAT FIRMLY AGAINST OPPOSITE END WALLS OF THE CAVITY WITH MOST OF THE OPENING THROUGH THE CORE EXTENDING ABOVE THE SURFACE OF THE PLATE; AND (C) ETCHING A SMALL APERTURE THROUGH THE BACKING LAYER INTO EACH OF THE CORE CAVITIES FOR PORVIDING A PASSAGEWAY FOR THE WITHDRAWAL OF AIR FROM THE CAVITY FOR HOLDING THE CORES IN SNUG SEATING ENGAGEMENT WITHIN THE RESPECTIVE CAVITIES. 